Strictly speaking, on a UK registered ship or aircraft, or in the UK, it is an offence under the Wireless Telegrahy Acts to deliberately receive a radio transmission unless you have a licence, or that the transmissions are specifically exempt from needing one - these are transmissions by radio amateurs, duly authorised sound broadcasting station, transmissions in the Standard time and Frequency service, and transmissions in the Radio Determination service.
Article 17 of the international Radio Regulations (which is international law and a formal treaty) requires Administrations to "take the necessary measures to prohibit and prevent unauthorized interception of radiocommunications not intended for the genral use of the public".
So strictly, using an airband receiver is illegal anywhere except when it is being used for authorised purposes. Generally the authorities turn a blind eye to it, but 186 countries signed up to that treaty - including the US, who send a civil servant of Ambassador status to the conference to sign the treaty.